The present invention is directed toward a flexible sheet product for absorbing liquids and, more particularly, toward a method and apparatus for making a non-woven flexible sheet product for absorbing liquids using melt-blown microfibrous materials.
The general principal in xe2x80x9cmelt-blowingxe2x80x9d technology is to blow, or spray, a molten thermoplastic polymer or resin onto a moving screen. Typically, the thermoplastic polymer is extruded through rows of small, side-by-side orifices into a high-velocity gaseous stream where the extruded material is attenuated and drawn into microfibers. The turbulence created by the high-velocity gaseous stream entangles the microfibers to form a web of fibrous material that is deposited onto a collector, such as a moving screen. The screen includes a vacuum system behind it which sucks, or pulls, the molten polymer onto the screen. The vacuum system controls the amount of loft and the tightness, or strength, of the absorbent sheet product. The higher the vacuum applied, the less loft the product will have, but the tighter, and hence stronger, the product will be. As the vacuum decreases, the absorbent sheet product will exhibit more loft, but will generally become weaker. Typically, as the loft of the product decreases, so does its liquid absorption qualities.
In prior art melt-blown technologies, the molten polymer is sprayed onto a single moving screen at an angle that is generally perpendicular to the moving screen. A vacuum behind the screen pulls the sprayed polymer onto the screen as the molten polymer fiberizes and cures to form a flexible sheet product for absorbing liquids. Controlling the loft, and thus the absorption qualities, of the finalized product is effectuated by adjusting the amount of vacuum applied behind the screen and/or moving the sprayer closer to or further from the moving screen.
With these prior art, melt-blown technology processes, there is generally a limit as to the thickness of the product that can be obtained, while still exhibiting good loft and strength qualities. If a thicker product is desired, a first sheet product is manufactured and wound on a xe2x80x9cput upxe2x80x9d roll or otherwise temporarily stored. A second sheet product is then similarly manufactured and the first sheet product is unrolled, with the two bonded together using ultrasonic bonding, or other means of bonding absorbent sheet products together. Making such multiple layer sheet products are generally time consuming and costly.
The present invention is directed to overcoming one or more of the above-mentioned problems.
An apparatus is provided for manufacturing a flexible sheet product having liquid absorbent qualities. The apparatus generally includes first and second competing vacuum systems pulling air in substantially opposite directions into first and second moving screens, respectively. A molten polymer-based material, which is blown into the first and second competing vacuum systems, is pulled in substantially opposite directions onto the first and second moving screens. The liquid polymer-based material fiberizes as it is being pulled apart by the competing vacuum systems creating a web of fibrous material which cures to develop the flexible sheet product having liquid absorbent qualities.
Preferably, the molten polymer-based material is pulled onto the first and second moving screens at an angle other than 90xc2x0 relative thereto. The first and second moving screens may be made of polyester or steel.
The apparatus may further include first and second roller assemblies operational with the first and second moving screens, respectively, providing for the movement of the first and second screens in opposite rotational directions. The first and second screens are displaced in close proximity to one other defining a loft zone therebetween. The molten polymer-based material is blown toward the loft zone, and onto the first and second screens, generally in the center where the first and second screens are moving together. The molten polymer-based material blown into the loft zone is acted upon by the first and second competing vacuum systems and pulled in substantially opposite directions onto the first and second screens forming a flexible sheet product exhibiting liquid absorbent qualities.
In one form, each of the first and second roller assemblies includes drive rollers for adjusting the rotational speeds of the first and second screens.
In an alternate embodiment, the first and second moving screens include first and second condensers rotating in opposite rotational directions.
A method is also provided for manufacturing a flexible sheet product exhibiting liquid absorbent qualities. The method generally includes providing first and second screens moving in opposite rotational directions. First and second vacuums are provided behind the first and second screens, respectively, the first and second vacuums pulling air into the first and second screens, respectively. A loft zone is created between the first and second screens wherein air is pulled in substantially opposite directions. A molten polymer-based material is blown into the loft zone and pulled in opposite directions by the first and second vacuums onto the first and second screens, respectively, developing a web of fibrous material. The web of fibrous material is cured to develop the flexible sheet product exhibiting liquid absorbent qualities.
In one form of the inventive method, the web of fibrous material is developed and cured substantially simultaneously.
It is an object of the present invention to provide a reduced cost, flexible sheet product for absorbing liquids.
It is a further object of the present invention to produce a flexible sheet product for absorbing liquids having desired loft and tightness specifications, while eliminating the process of making xe2x80x9cput upxe2x80x9d rolls to achieve a desired product thickness.
It is yet a further object of the present invention to produce a flexible sheet product for absorbing liquids having improved loft and tightness qualities.
It is still a further object of the present invention to provide an apparatus for making flexible sheet products for absorbing liquids which offers improved loft controllability of the resultant flexible sheet product.
Other aspects, objects, and advantages of the present invention can be obtained from a study of the application, the drawings, and the appended claims.